docs: optimize README for v0.8.0

- Remove all PWA references (PWA was removed in v0.8.0)
- Move Android app section to 'Mobile App' near bottom
- Create proper markdown table of contents
- Update tech stack to reflect current stack (React Query, TypeScript, Zod)
- Remove PWA column from Tested Systems table
- Convert configuration and security sections to tables for clarity
- Improve overall structure and readability

Author: IT-BAER